Transformer Secondary Conductors

[wlthorpe]

Struggling to completely understand the bounding and grounding around transformer and sizing of neutrals leaving the secondary. From what I understand in most real world scenarios the neutral conductor will be sized to the expected load or to the same size as the ungrounded conductors. All of that aside to abide by the NEC minimum requirements, the size requirements are found in table 250.102(c)(1)....
So in a single raceway with 3- 3/0 ungrounded conductors leaving a transformer, I would size my Neutral/grounded conductor in accordance with the table and be left with a #4 minimum size?
In that same raceway I would also have a #4 supply-side bonding jumper?
If so would this remain the same regardless of me terminating the system bonding jumper in the transformer enclosure or the secondary panel enclosure?
Thanks for any info.

 

[tom baker]

The first time I installed a step down transformer, I slowly reviewed the rules in Art 250, that helped me a lot. It’s quite a section, but you will get some good answers here. I will post a few graphics later today
Welcome to the forum. Don’t hesitate to ask as we all learn

 

[augie47]

Your interpretation sounds correct.
Keep in mind along with your grounded conductor and SSBJ you need the System Bond Jumper.

 

[tom baker]

That’s the graphic I was going to post. It’s your choice on where to install the SBJ. I did the SBJ at tranny for small transformers with wire leads
Note the GEC connection is made where the SBJ is located.
There is a minimum size of the EGC and neutral, depending on how the xfmr is wired